The present disclosure relates to engine heat management systems and more particularly to engine fuel-oil heat exchangers, for example as used in gas turbine engines.
It is known for aircraft engines, and gas turbine engines more generally, to provide a fuel-oil heat exchanger such that heat energy transferred to the oil as it flows through hot portions of the engine can be transferred to the fuel prior to combustion, so as to improve cycle efficiency. Heat energy is typically transferred to the low pressure side of a fuel system, i.e. upstream of a fuel pump and fuel metering unit that control fuel flow to the engine combustor.
It is also known that excess heat energy may need to be dumped from the oil system by the use of one or more air cooler to prevent fuel temperatures becoming overly elevated. A conventional heat management system thus allows oil flow to selectively bypass one or more air cooler.
Ongoing efforts to improve the efficiency of gas turbine engines can result in less energy being available to heat the fuel. If fuel is not sufficiently heated it has been found that ice crystals can form, and reside, within the fuel flow.
Whilst the ice crystals are of generally small enough size to be accommodated in the flow to the combustors (i.e. the primary use of the fuel flow), problems have been found to occur where the fuel flow is used to drive ancillary equipment, such as hydraulic actuation systems (i.e. the secondary use of the fuel flow). In particular, certain high tolerance components such as servo valves and the like require small flow openings/clearances for which icing due to the ice crystals in the fuel flow can present a significant potential blockage.
It is an aim of the present disclosure to provide an engine fuel-oil heat exchange system that offers greater control. It may be considered an additional or alternative aim to provide an engine fuel-oil heat exchange system that can better safeguard temperature-sensitive equipment.